Flex PCBs Make Force-Mapping Pressure Sensor For Amputee

April 9, 2019 by Dan Maloney 1 Comment

What prosthetic limbs can do these days is nothing short of miraculous, and can change the life of an amputee in so many ways. But no matter what advanced sensors and actuators are added to the prosthetic, it has to interface with the wearer’s body, and that can lead to problems.

Measuring and mapping the pressure on the residual limb is the business of this flexible force-sensing matrix. The idea for a two-dimensional force map came from one of [chris.coulson]’s classmates, an amputee who developed a single-channel pressure sensor to help him solve a painful fitting problem. [chris.coulson] was reminded of a piezoresistive yoga mat build from [Marco Reps], which we featured a while back, and figured a scaled-down version might be just the thing to map pressure points across the prosthetic interface. Rather than the expensive and tediously-applied web of copper tape [Marco] used, [chris] chose flexible PCBs to sandwich the Velostat piezoresistive material. An interface board multiplexes the 16 elements of the sensor array to a PIC which gathers and records testing data. [chris] even built a test stand with a solenoid to apply pressure to the sensor and test its frequency response to determine what sorts of measurements are possible.

We think the project is a great application for flex PCBs, and a perfect entry into our Flexible PCB Contest. You should enter too. Even though [chris] has a prototype, you don’t need one to enter: just an idea would do. Do something up on Fritzing, make a full EAGLE schematic, or just jot a block diagram down on a napkin. We want to see your ideas, and if it’s good enough you can win a flex PCB to get you started. What are you waiting for?

A Guide For Driving LED Matrices

November 27, 2018 by Bryan Cockfield 8 Comments

Building an LED matrix is a fun project, but it can be a bit of a pain. Usually it starts with hand-soldering individual LEDs and resistors together, then hooking them up to rows and columns so they can be driven by a microcontroller of some sort. That’s a lot of tedious work, but you can order an LED matrix pre-built to save some time and headache. You’ll still need a driver though, and while building one yourself can be rewarding there are many pitfalls and trade-offs to consider when undertaking that project as well. Or, you can consider one of a number of drivers that [deshipu] has outlined in detail.

The hangups surrounding the driver board generally revolve around the issue of getting constant brightness from LEDs regardless of how many in the row or column are illuminated at one time. Since they are typically driven one row or column at a time, the more that are on the lower the brightness each LED will have. Driver boards take different approaches to solving this problem, which usually involve a combination of high-speed scanning of the matrix or using a constant-current source in order to eliminate the need for resistors. [deshipu] outlines four popular chips that achieve these purposes, and he highlights their pros and cons to help anyone looking to build something like this.

Most of these boards will get you to an 8×8 LED matrix with no problem, with a few going a few pixels higher in either direction. That might be enough for most of our needs, but for something larger you’ll need other solutions like the one found in this 64×32 LED matrix clock. There are also even more complicated drivers if you go into extra dimensions.

Photo credit: Komatta [Public domain], from Wikimedia Commons

Clock Plays A Game Of Pong With Itself To Pass The Time

June 24, 2018 by Dan Maloney 4 Comments

Would you play a game of Pong where each set lasts exactly one minute and the right player is guaranteed to win 60 times more than the left player? Of course not, but if you were designing a clock that displays the time using a Pong motif, then perhaps it would make sense.

There are some neat design tips in [oliverb]’s Pong Clock that are worth taking a look at. Foremost is the case, which is a retasked jewelry box with a glass lid, procured on the cheap from eBay. It’s a good size for a clock meant to be seen from across the room, and already finished to fit into modern decor. The case holds all the goodies, from the 24×16 green LED matrix display to the Uno that runs the show, as well as an RTC module, a sound chip, a temperature sensor, and a PIR module to turn the display off when the room is unoccupied. To prevent disrupting the sleek lines of the case, all the controls are mounted in a remote panel, itself a clean and modern-looking device thanks to the chrome-plated duplex outlet cover used to house it. The clock has several display modes, from normal time and temperature to a word clock, as well as the Pong mode, where the machine plays itself and the score shows the time. It’s fascinating to watch, and we like everything about it, although we think the tick-tock would drive us nuts pretty quickly.

We recently covered the life and times of [Ted Dabney], one of Pong’s fathers and co-founder of Atari. We tend to think he’d like the design of this clock, both as a nod to his game and for its simple but functional design.

Continue reading “Clock Plays A Game Of Pong With Itself To Pass The Time” →

A YouTube Subscriber Counter With A Tetris Twist

June 19, 2018 by Dan Maloney 1 Comment

When it comes to YouTube subscriber counters, there’s not much wiggle room for creativity. Sure, you can go with Nixies or even more exotic displays, but in the end a counter is just a bunch of numbers.

But [Brian Lough] found a way to jazz things up with this Tetris-playing YouTube sub counter. For those of you not familiar with [Brian]’s channel, it’s really worth a watch. He tends toward long live-stream videos where he works on one project for a marathon session, and there’s a lot to learn from peeking over his virtual shoulder. This project stems from an earlier video, posted after the break, which itself was a condensation of several sessions hacking with the RGB matrix that would form the display for this project. He’s become enamored of the cheap and readily-available 64×32 pixel RGB displays, and borrowing an idea from Mc Lighting author [toblum], he decided that digits being assembled from falling Tetris blocks would be a nice twist. [Brian] had to port the Tetris-ifying code to Arduino before getting the ESP8266 to do the work of getting the subs and updating the display. We think the display looks great, and the fact that the library is open and available means that you too can add Tetris animations to your projects.

None of this is to say that more traditional sub counters can’t be cool too. From a minimalist display to keeping track of all your social media, good designs are everywhere. And adding a solid copper play button is a nice touch too.

Continue reading “A YouTube Subscriber Counter With A Tetris Twist” →

Is That A Tweet On Your Belt Buckle Or Are You Just Happy To See Me?

May 8, 2018 by Dan Maloney 8 Comments

What a time to be alive! The range of things you never knew you needed but absolutely must have expands at a breakneck pace, such that it’s now possible to pick up a belt buckle with an embedded LED matrix to scroll messages. We have no idea what the use case for something like this is, but some people will buy anything.

One such person was a friend of [Brian Moreau], who doubled down after being gifted the glowing bauble by turning it into a WiFi enabled Tweet-scrolling belt buckle. It appears to be a just for fun project, and to be honest one would need a heck of a belt for the buckle after his mods. He added an ESP8266 to take care of monitoring his Twitter account and driving the display on the belt buckle, a non-trivial task given that the thing is programmed with only two buttons that scroll through characters to compose a message. The microcontroller might have fit inside the original buckle or only added a little to its bulk, but [Brian] decided to replace the two coin cells powering it with an external 6-volt battery pack. That required a buck converter to power the ESP, so the whole thing ended up being thrown in a case and acting more like a neat display than a flashy fashion statement.

We’d bet some tradeoffs could be made to reduce the bulk and get that buckle back where it belongs, though. Once it does, maybe it’ll be part of a complete LED-laden ensemble, from head to toe.

Marquee Display Uses Six Dozen Surplus VFD Tubes To Great Effect

April 19, 2018 by Dan Maloney 6 Comments

The quest to repurpose surplus parts into new and interesting displays never ends, it seems. And the bigger the display, the better, with extra points for using some really obscure part, like these surplus Russian vacuum-fluorescent tubes turned into a marquee display.

As [tonyp7] freely admits, this is a pet project that’s just for the fun of it, made possible by the flood of surplus parts on the market these days. The VFD tubes are IV-25s, Russian tubes that can be had by the fistful for a song from the usual sources. The seven small elements in the tube were intended to make bar graph displays like VU meters, but [tonyp7] ganged up twelve side by side to make 84-pixel displays. The custom driver board for each matrix needs three of the old SN75518 driver chips, in 40-pin DIPs no less. A 3D-printed bracket holds the tubes and the board for each module; it looks like a clock is the goal, with six modules ganged together. But the marquee display shown below is great too, and we look forward to seeing the finished project.

From faux-Nixies made with LEDs to flip-segment displays driven by relay logic to giant seven-segment LEDs that can be 3D-printed, we really like the trend to unique displays. What are you dreaming up?

Continue reading “Marquee Display Uses Six Dozen Surplus VFD Tubes To Great Effect” →

Automating The Design Of Word Clocks

April 17, 2018 by Brian Benchoff 9 Comments

Word clocks, or a matrix of light-up letters that spell out the time, are a standard build for all enterprising electronics enthusiasts. The trouble is finding the right way to drive a matrix of LEDs and the significant amount of brainpower that goes into creating a matrix of letters that will spell out the time without making it look like it’s supposed to spell out the time.

For his Hackaday Prize entry this year, [Stephen Legge] is creating a standard toolkit that makes word clocks easier to build. It’s a hardware and software project, allowing for LED matrices of any reasonable size, and the software to make a grid of letters that only spells out the words you want and not the four-letter ones you don’t.

The hardware for this project is built around the IS31FL3733 LED driver from ISSI. This is an interesting chip that takes I2C in and spits out a LED matrix with very few additional support components. This chip provides [Stephen] with a 12×16 single-color LED matrix, which is more than enough for a word clock.

Where this build gets slightly more interesting is the creation of a custom matrix of letters that will still spell out ‘quarter to noon’ when lit in the appropriate way. This is a big challenge in creating a customized word clock; you could always borrow the layout of the letters from another word clock, but if you want customized phrases, you’ll either have to sit down with a pencil and graph paper, or write some software to do it automatically.

It’s a great project, and since all of [Stephen]’s work is being released under Open Source licenses, it’s a great entry to the first portion of the Hackaday Prize where we’re challenging hardware creators to build Open Hardware.